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# Combinatorics and Probability cheat sheet !

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Intern
Joined: 17 Jan 2018
Posts: 3
Combinatorics and Probability cheat sheet !  [#permalink]

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09 Oct 2018, 09:02
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Combinatorics

* Permutation formula: $$^nP_r$$ = $$\frac{n! }{ (n-r)!}$$

* Combination formula: $$^nC_r$$ = $$\frac{n! }{ (r!)*(n-r)!}$$

* $$^nP_n$$ = n!

* $$^nC_r$$ = $$^nC_n_+_r$$

* The number of ways in which n things can be arranged taking them all at a time where p things are exactly the same,q things are exactly the same and r
things are exactly the same.

= $$\frac{n!}{p!*q!*r!}$$

* The number of ways of selecting one or more items from n given items

= $$2^n$$ -1

EXTRA FORMULAS

* The number of ways of dividing (p+q) items into two groups of p & q items respectively

= $$\frac{(p+q)!}{p!*q!}$$

Probability

Probability = $$\frac{Number of favorable outcomes }{Number of all possible outcomes}$$

Probability of events A & B happening = Probability of A * Probability of B

Probability of either event A or B happening = Probability of A + Probability of B
Senior Manager
Joined: 18 Jun 2018
Posts: 263
Re: Combinatorics and Probability cheat sheet !  [#permalink]

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12 Oct 2018, 05:57
chirayuvyas97

Thanks for cheat sheet
Re: Combinatorics and Probability cheat sheet !   [#permalink] 12 Oct 2018, 05:57
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